CSS dynamic width aspect ratio

Positioning a centered video iframe on a responive website only knowing the 16:9 aspect ratio but no fixed size?

Your CSS code (in less syntax):

.videoframe{position:absolute;top:10%;left:25%;border:2pxsolid#ffffff;width:50%;.outer{width:100%;padding-top:56.25%;/* 16:9 ratio, at 4:3 it will be 75% */position:relative;.inner{position:absolute;top:0;left:0;right:0;bottom:0;}}}